For many educational, laboratory, medical, research or industrial purposes, it is frequently desirable to study migration of a substance in a suitable retarding medium and/or to effect separation of complex substances by differential migration in such media.
When the driving force inducing the migration is an electric field and the medium is capable of retarding the movement of a component as a function of its molecular weight, charge and molecular size, the method is known as electrophoresis and, where separations are carried out in other ways, the methods may be various chromatographic techniques.
In all of these methods a medium is provided through which the components to be separated move at different velocities under various driving forces and with the medium being oriented differently, depending upon the purpose and the technique.
While the background of the invention will be described in connection with horizontal gel electrophoresis, therefore, it should be understood that horizontal gel electrophoresis represents the best mode currently known to us for utilizing the invention, i.e. carrying out the invention in practice. However, in its broadest sense, the invention may involve merely the study of migration of a substance in an appropriate medium or the differential separation of substances in a medium basically utilizing the same device and hence such uses are not excluded except as we have otherwise limited them in the description and the appended claims.
As noted, electrophoresis is an analytical method widely used in research and increasingly advantageous for clinical and analytical processes. While the art recognizes a variety of electrophoresis devices and methods, e.g. thin-film and column electrophoresis, the type of electrophoresis with which the invention is principally concerned can be termed horizontal gel electrophoresis.
Even in conventional systems of the latter type, complex equipment, manipulations and procedures were involved. Generally a gel was cast into slabs and the ends of each slab connected with vessels containing appropriate buffer solutions and forming conductors between the gel and the electrodes.
The electrodes are connected to opposite poles of a high voltage source, the material to be separated, with or without prior treatment, was placed upon the slab and the substances within this material migrated with different velocities, depending inter alia upon molecular weight, or at different rates under the electrical driving force applied across the slab.
The prior art devices for this purpose have been fairly complex and because of their complexity required reuse with many disadvantages. For example, the identification of the substances separated across the gel layer is usually carried out with a so-called developer having or producing a predetermined color depending upon the nature and concentration of the substance under investigation, i.e. the developer can be an indicator-type dye or forms such a dye. Even traceamounts of developers of this type present in the system may create interference with subsequent runs of a test, experiment or analysis unless the device is thoroughly cleaned since the earlier devices were not replaceable because of high cost.
Even when the unit appeared to be clean, trace amounts of the developer can create problems and hence the gel slab was frequently removed from the device prior to development simply to avoid contamination.
Because of the need to remove gel slabs for development, the gel slab had to have sufficient density so that its coherency could permit the removal. This, of course, reduced the diffusion rate for which it could be designed.
It was also necessary to form this slab with relatively large minimum thickness so that the slab could tolerate the manipulations required without deterioration.
In part because of these limitations, earlier horizontal gel electrophoresis was not fully sucessful. The manipulator steps discussed above were also found to introduce errors in the migration by surface distortion and the like and extremely precise determinations could not be made.
Washing techniques, which did not always prove to be successful for the reasons mentioned, also required a long down-time of the apparatus.
In addition, because of the requisite thickness for the gel slab and to avoid deterioration in contact with the buffer electrolyte, the bars bordering the gel slab in the region of the electrodes remained in place for the entire operation which means that communication passages were requested between the gel and the buffer. These passages create sites for the preferential passage of the electric current which caused local temperature differences interfering with the uniformity of the action. Furthermore, higher voltages were often required because of the interruption of the zones of contact between the buffer and the gel slab.
A conventional apparatus of this type is even more difficult to employ when radioactive materials are studied because the radioactivity accumulates in portions of the apparatus and can give rise to parasitic signals or noise which falsify the results. Simple disuse, of course, is impractical because the electrodes frequently are composed of a precious metal such as platinum.
Disposable trays for the gel slab have been provided heretofore in an effort to avoid some of the aforementioned problems. Such trays cooperate with an electrode tank carrying the electrodes and the buffer electrolytes and forming a unit separate from the tray. The latter tank can be placed on top of the tray with the electrolyte communicating with the gel in the tray.
This argument certainly eliminates the problems of distortion of the slab and the problems described above in connection with the handling of the slab away from the other elements of the apparatus.
Nevertheless this system was involved in a number of problems. For example for each replacement of a tray containing a slab, it is necessary to lift the electrode carrier and replace the electrode carrier. For a single reaction or run this does not create any particular difficulty but when a number of runs is required, it is necessary to provide either a multiplicity of electrode carriers or to clean the electrode carriers between each use. Furthermore, the electrode carrier, when in use for one tray, cannot be utilized for a second tray. Since the electrode carriers, tanks, etc. are complex and expensive, multiplying the number of them in a laboratory poses a significant problem. In addition, these systems do not avoid the difficulties with radioactive materials previously mentioned.